Northstar Engines and System Technical Discussion Discussion, Northstar Headgasket/Cracked Block/Bolt Failure? Please let us know in Cadillac Engine Discussion; Originally Posted by xeper
Hmmmm, this COULD have something to do with it:
If this led to some sort of ...

1996 Seville SLS at 132,000 miles. Two previous cooling problems precipitated the final failure; Impeller and radiator went out.. The OAT orange coolant starts eating the gaskets from within, once air ever gets in the system.

Same thing happened to my 2000 Chevy Venture. Did a top end to that engine, and started using green coolant and all cooling problems fixed.

As for my 1996 SLS, I have not yet decided if I'm going to time-sert the block, get a used engine, look at the LS4 5.3 transverse engine swap, or just take this beautiful car to the junk heap and call it quits. No one seems to want to buy a good looking car with any problems. Still runs like a sewing machine, but you can smell coolant from the exhaust and overheating is a crap shoot. 5 miles or a 100 miles, ... it is unpredictable except that it will overheat.

Is an LS4 swap viable? A friend of mine wants to know, his N* is starting to use coolant (steamy exhaust, makes a nice cloud at times). I am pretty sure it hasn't come close to overheating, he bought a new Jeep so the Cad is now parked.

He has a 99-00 SLS. He wants to get it back up and running, I mentioned a LS4 swap is possible, but we need to know details.

Re: Definitive Northstar Headgasket Thread

Originally Posted by creeker

What actually is the cause of the head bolts pulling out?, is it caused by old coolant?.

Can someone tell me if the Northstar uses a torque-to-yield headbolt system?

I'm curious because the headbolts on my mucho expensive BMW V12 failed at 62k due to use of that system. I'm wondering if Cadillac didn't engineer itself into the same corner. BMW eventually fixed the issue (took it 5 years of production, through). As far as I can tell, every mfg who has used this system, be it GM, BMW, Honda, or whomever, ends up with blown gaskets due to failed headbolts.

I think mfg's are engineering themselves into corners because marketing departments want to wow customers with technology and performance, but this comes at a price in longevity. A 12v cast iron V6 can be made to last forever even with minimal maintenance, but nobody wants one in their car anymore. So we get highly stressed, high tech engines that are zippy and give good mpg off the showroom floor, but are prone to failure. GM is not the only mfg in this corner.

To make it worse, the heavy use of leases means most of those "buying" the cars don't give a hoot about how long it will last after 4 years--they're just going to hand it to the dealer and get a new one anyway. So why build the car to last 150k? To please a bunch of folks who never buy new anyway?

So basically the failure mode is coolant leaks into the threads of the head bolts, corrodes the block, and the head bolts give way and you are done. So somehow you need to absolutely prevent coolant from ever getting to the threads.

What did BMW do it to fix?

GM should revisit the main bolt concept on the 427 Hemi Pontiac. They had spayed main bolts and the lower head bolts were long and went into the main caps. The upper head bolts went into the block deep, well past where the bores were so no bore distortion could happen when the heads were tightened down. This is a long Pontiac design already on the top bolts, but the bottom never got into production.

So basically the failure mode is coolant leaks into the threads of the head bolts, corrodes the block, and the head bolts give way and you are done. So somehow you need to absolutely prevent coolant from ever getting to the threads.

What did BMW do it to fix?

Well, then the failure mode is not similar to BMW's. With the BMW, the head bolts were purposefully stressed to the point of stretching and using the elastic properties of the metal to compensate for expansion of the all-aluminium block and heads. Sort of like holding the heads with really strong rubber bands. Probably works great in a Formula One engine intended to last 400 miles. Not so great for a passenger car engine. The bolts would stetch a bit too far and couldn't return to their previous length. When I pulled my head bolts, average torque remaining in the bolts as about 35 ft lbs, due to this overstretching.

Ask a mechanical engineer about the stress-strain curve, the yield point, and the modulus of rupture.

Sounds like the Northstar is more similar to the old Jaguar 6. As Jag expanded the displacement over the years they extended the head studs deeper into the block to the point the studs ran through the water jacket. If you didn't keep the coolant super clean the studs would corrode. The engines were so dammed overbuilt that you probably still wouldn't lose a gasket, but it was hard to remove the stud without leaving 1/2 the stud behind if you ever had to pull the head.

Does the Northstar expose the head bolt directly to coolant or does failure first require something else, like a cracked waterjacket or a partial loss of seal at the headgasket?

Sorry, I didn't phrase it well, I am guessing that is the problem, not sure if it is. A lot of people seem to blame the antifreeze so that is my guess.

I sure would like to know the actual engineering analysis for the failures. And is it repairable to make the engine truly reliable.

I am worried on my mom and dad's 97, they are @ 105K on GM installed antifreeze...... I found a trace of coolant on one sparkplug, so I am concerned they are on borrowed time.... The car doesn't drive much anymore, but still gets driven several times a week....

Actually, the "explanation" of antifreeze corroding the bolts makes perfect sense. The overall problem still sounds much like what I've seen with the Jag 6, through the problme is not limited to that engine and is a fundamental issue with any aluminum motor.

The basic issue is that because of the greater expansion of aluminum, an all-aluminum design puts much more stress on the head gasket--it gets squeezed tighter when the engine is warm and has to expand more to fill in the gaps when the engine is cold. After 1000's of cycles, the gasket will lose some of it elasticity and no longer seal completely. Small leaks from the water jacket result, and if the antifreeze is old, the headbolts (which are iron or other metal susceptible to corrosion) will corrode and eventually fail.

With the Jag, the solution was to change the headgasket at 100,000. You didn't wait for a failure; this was considered normal maintenance. The good part was that the engine was so overbuilt that you only changed the gasket--the timing chain, valve seals, etc., were good to 150k easily.

BMW (and others) have tried to avoid this problem by designing the head bolts so they stretch and take some of the load off the gasket, which can be made out of very hard and tough material. I still have one out of my V12, and it likely is vulnerable only to A-bombs and cockroaches

Us red blooded 'mericans are used to driving cast iron blocks and head forever without head gasket issues. Those times are gone.

I wonder if GM when the extra mile with the STS-V and used a better gasket material?

But is better gasket material gonna fix anything? Or prolong the inevitable?

Makes me wanna avoid any alum block cars out of fear of headaches.

Are the LS1's, LS2's, LQ9's, LS7's and the like having any issues? They make a lot more power in many cases, did they fix it with them?

Well, the new Vette ZR-1 has a 4-layer gasket rather than a 2-layer gasket, so I suspect a mfg can spring for extra $$ and prolong engine life. Don't forget that for decades GM used rubber o-rings as valve seals on the small block chev. The General is not above scrimping on key engine parts.

As for all-aluminum designs, I'll just say there's a reason that my other car is a Buick with the good 'ole cast iron 12v V6. Simple and near indestructable.

And don't hesitate to post even if you got rid of the car. I wish I could post for my 94 but I sold it without diagnosis so it may have just been a coolant leak. In my opinion dex cool is the culprit behind the issue. If you kept the coolant clean in pre dex cool as my 94 was it ran forever. I got rid of mine at 187k and running like new minus the coolant leak. I also plan to drain and refresh my coolant every spring to make sure my coolant is always fresh and not harmful. That and it only takes a bottle to fill it and costs 8 bucks from wal mart.